As an alternative or as an addition to the treatment of heart rhythm disorders, it has been proposed that certain troubles of myocardial contraction observed in patients with heart failure be treated by biventricular pacing, whether the troubles are spontaneous or induced by traditional pacing. Reference is made to the study by J. C. Daubert et al., published in Stimucoeur, 25, n°3, on pages 170-176, which presents a summary on the studies made on that topic. This CRT therapy has allowed one to observe most of time astonishing results for patients with class III heart failure, who are not improved by usual treatments.
One such CRT pacemaker is for example described in European Pat. EP-1 108 446 and its counterpart U.S. Pat. No. 6,566,866 (commonly assigned herewith to ELA Medical), which disclose a device allowing to apply a variable interventricular delay between two ventricular pacing pulses, adjusted so as to resynchronize contraction of the ventricles, with a fine optimization of the patient's hemodynamic status.
Most of the CRT devices used nowadays are so-called “mutisite” prostheses, in which the electrodes are positioned in a plurality of distinct respective sites, comprising at least one atrial site in addition to left and right ventricular sites, as in “triple-chamber” prostheses (dual ventricular pacing and right atrial sensing/pacing) or “quadruple chamber” prostheses (dual ventricular pacing and dual atrial sensing/pacing).
The physical location of endocardial electrodes in relation with myocardial tissue will be hereinafter referred to as “pacing sites”; usually, these sites can only be chosen during the implantation procedure, through an appropriate positioning of electrodes. It is important to make sure of the efficacy of the chosen sites, because of the potential influence, with a long term perspective, on the resynchronization therapy. In some cases, the multisite device has plural electrodes placed in the same cavity, giving one an opportunity to modify the pacing site in that cavity, by internal commutations of the device between said electrodes.
Hereinafter, reference to “pacing sequence” is to firstly, the order along which the pacing pulses are delivered to the heart (for example: first the atrium, then left ventricle, then right ventricle), and secondly, the time intervals separating delivery of those successive pulses. The pacing sequence is parameterized during the implantation procedure, and may further be modified, if need be, through appropriate internal commutations of the device and adjusting the parameters of pulse sequencing.
Hereinafter, reference to “pacing configuration” is to the combination of the characteristics relating to “pacing sites” and those relating to “pacing sequence”.
The invention is proposing a solution to the problem, as recognized by the inventors, of optimizing biventricular pacing through selection of the most appropriate pacing sites and the best sequence for pacing these sites. This optimizing is of course performed during the implantation procedure, but may advantageously be performed again at periodic or aperiodic intervals, in order to follow up the course of the patient's general hemodynamic status, particularly during phases of improvement or degredation of the condition of the myocardium.
There are currently existing various means for assessing the degree of efficacy of biventricular pacing. Most of them consist of echographic techniques, which always have to be performed by qualified personnel in hospital environment. For that reason they are costly, and cannot be utilized as often as it could be useful or necessary, without interfering with the patient's daily life.
EP-1 108 446 and U.S. Pat. No. 6,566,866 referred to above propose a solution that consists of assessing the degree of synchronization of left and right ventricles contractions, through measurement of intracardiac bioimpedance, data representative of cardiac output and therefore ejection fraction, considered as being the reference hemodynamic parameter.